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What is virtual colonoscopy?
Virtual colonoscopy is a technique that uses a computerized tomographic (CT) scan (a type of three-dimensional x-ray) to construct virtual images of the colon that are similar to the views of the colon obtained by direct observation by optical colonoscopy.
In preparation for virtual colonoscopy, the day before the examination the colon is emptied using laxatives in a manner similar to optical colonoscopy. During the examination, a small tube is inserted into the anus to inject and fill the colon with air. Unlike with optical colonoscopy, this tube is not advanced into the colon. The CT scan then is performed, and the scans are manipulated by computer software to form virtual images of the colon. When properly performed, virtual colonoscopy can be as effective as optical colonoscopy. It can even find polyps "hiding" behind folds that occasionally are missed by optical colonoscopy. The scanning takes only 10 minutes, and usually no conscious sedation is necessary.
In October, 2007, researchers from University of Wisconsin published in the New England Journal of Medicine a study comparing traditional optical colonoscopy to virtual colonoscopy. More than six thousand patients over age 50 were evenly divided to undergo either optical or virtual colonoscopy. The researchers found that virtual colonoscopy was as effective as optical colonoscopy in detecting polyps larger than 5mm.